Hit Rating/Expertise

So, i was taking a look at DREAM Paragon's main team warlock Verdisha and noticed that on his gear, he socketed +160 Expertise +160 Mastery gems on his red sockets instead of the "traditional" +80 Int +160 Mastery. His spec is Affliction.

After this i was left wondering:
Does Expertise points equal hit rating simply put, or is there some internal mechanic/some math to it?
Does Expertise have any advantage over Hit rating?
Wouldn't it be theoretically better to gem int+mastery and get the remaining hit rating we need from reforging instead of sacrificing a major stat?

Sadly RAWR isn't working with warlocks atm for me to play around with gems, and honestly i wouldnt know how to tackle the situation, expertise on warlocks is still something new to me..

Expertise rating for spells now works exactly the same as having hit rating. The reason you see him gemming expertise in some slots and hit in others is simply to match socket colors for bonuses.

Gemming Int/mastery sounds like it should be the logical thing to do, but I just ran a small sim on his character coming up with rough stat weights of 4.25 for Int, and 2.23 for mastery. Now that gems provide double the secondary stats as they do primary, you can simply double the 2.23 and see that it beats out his weight for Int. And finally, why he is using gems for hit as well is that he can then reforge his gear to gain that much more mastery.

I see that makes sense, the more points we have over the hit cap, the more hit we can reforge into other things... But the hit you gain from expertise automaticaly shows up at Hit Rating or it is shown at the Expertise part and we need to add it?

Plus, what tool did you use to check the weight of each stat against another? That would be really useful (i've only used RAWR but it is not functional for warlocks in this patch yet..)

Just so you don't find yourself getting a lot of conflicting numbers, I suggest reading/watching one of the various guides you can find on how to set up simcraft. For example the default iterations is set at 1000, which isn't enough to derive stat weights from, you want it to be at least 10,000. http://www.wowhead.com/guide=100/sim...your-character is a an example of one that you can quickly skim over to see how to set up the various options.

Thanks again, i'll take a loot at it before going headfirst into simcraft

EDIT, 1 day after original post:

So, after toying around with SimCraft, and filling all gem slots with expertise/mastery gems like there's no tomorrow and reforging accordingly, i simmed both before and after gearsets (25k times each) and what would you know?! Not gemming into Int at all on red sockets in favour of expertise actually increased my dps! Madness! xD